Automatic control apparatus



" June 2- A. E. KROGH 2,285,288

AUTOMATIC CONTROL APPARATUS K Filed April 15, 1938 6 Sheets-Sheet 1 mmvroa ANKER EQKROGH ATTORNEY 1938 6 Sheeta-Sheet 2 A. E. KROGH AUTOMATIC CONTROL APPARATUS Filed April. 15,

' Jgne 2. 1942.

mvzvma. ANKER' E. KROGH uni June 2, 1942. A. E. KROGH AUTOMATIC QONTROL APPARATUS Filed April 15,' 193 '6 sheets-sheet 3 Illlllll uuuw' FIG.2A.

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ANKER E. KROGH V A RNEY.

A. E. KRdGl-l June 2, 1942.

AUTOMATIC CONTROL APPARATUS Filed April 15, 1938 6 Sheets-Sheet 4 -lllllllv- INVENTOR. ANKER E. KROGH A RNEY.

June 2,1942. .A. E. KROGH 2,285,288

Amer/kins CONTROL APPARATUS Filed April 15, 1938 6 Sheets-Sheet '5' f I INVENmRQ v q ANKER E. KROGH q g June 2 1942.

A. E. Kw )GH AUIOMATIQ comixbz, .urrnmms '5 Sheets-Sheet 6 Filed April 15, 1938 INVENTOR.

KROGH v/ /127) 7/. II

FIG.

ANKER E.

j UNITED STAT M particularity in the claims annexed 'atentediJune 2, 1 942 as PAT-ET 'FFICE 7 Anker E. Krogh, Philadelphia, Pa, assignor to The Brown Instrument Company, Philadelphia, Pin, a corporation of Pennsylvania Application April 15,1938, Serial No. 2023071 4 Claims.

This inventionrelates to automatic controlv apparatus and especially to the automatic con trol of metallurgical furnaces'such as soaking pits and the like, in which large ingots of steel or othermetal are heated preparatory to a rolling or other subsequent processing operation.

In the control of. soaking pits and other metallurgical furnaces; it is desirable to heat the the pit. The products of combustion thereafter move downward along the vertical pit walls and exhaust through a plurality of ducts, the path of the gases thereby substantially surrounding the charge. The soaking pit may be of the type shown and described in Morton et al. Patent Number 2,079,560. The regulation of the supply of'fuel and air to the pit burner shouldbe carried out in such a manner as to prevent the attainment of an excessive temperature by the ingots, to the endof preventing washing or burning, of the ingot oxide coating or scale, such washing being undesirable both from the standpoint of the loss of metal, and increased frequency of pit repair,

give rise to imperfections in the subsequently fabricatedmetal. On the-other hand, relatively high ingot temperatures must be finally attained and sometimes held for a period in order to pre- "charge to the desired temperature with a minimum'consumption of fuel, in the quickest possiunderstanding of the invention, its advantages,

and specific objects attained with its use, refer ence should be had-to the accompanying drawings'and descriptive matter in which I have illustrated and described preferred embodiments of the invention.

f the drawings,

Fig. 1 is a more or less diagrammatical view of one embodiment of the invention;

Fig. 1A is a more or less diagrammatical view showing one modification of the invention;

Fig. 1B is a more or less diagrammatical view showing another modiflcation of the invention;

, and also because severe cases of washing may pare the ingots for rolling or. the like, and this operation should. in the interest of fuel; economy, steel structure and 'mill efflciency, be carried out as rapidly and uniformly as possible.

In order to attain uniform heating of all the charge to the desired temperature, including the portions most remote from the heating medium, and without overheating'or washing any portion of the charge, I control the fuel supply to the furnace in significant response to the portion of the charge most remote from the source of heat, as wellas in significant response to the portion of the charge most likely to be overheated.

The various'ieatures of novelty which characterize the present invention are pointed out with to, and'forming a part of this specification, but for a better Fig; 1C is a more or less diagrammatic view showing still another modification of the inven-v tion; i

Fig. 2 is a detailed fragmentary view, partially diagrammatical, of apparatus shown in Fig. 1; 1

Fig. 2A is a detailed modificationof a portion of Fig. 2;

Fig. 2B is a detailed portion of Fig. 2;

Fig. 3 is a diagrammatical view of another embodiment of the invention;

Fig. 4 is a diagrammatical view of' still another modification of another embodiment of the invention; and

Fig. 4A is a sectional view takensubstantially.

along theline lA-lA of Fig. 4;

Fig. 5 is a diagrammatical view of alternate g riipazatus for carrying out the embodiment of g. 7 Referring first to Figs. 1, 4 and 4A. a soaking pit C is illnstrated which has fuel gas ducts D supplied-from a common main D, whereby fuel is supplied to a burner port I) at the bottom of the pit. Combustion supporting air is supplied through ducts C and recup'eratcrs C one at each side of pit or chamber C to the chamber, Such air may be mixed with the gas fuel before the latter leaves burner portD, as in Fig. 1. Products of combustion pass from the chamber C? t the waste gas passages of recuperators C through outlet ducts C and pass therefrom to the-stack or "exhaust pipe C (Fig.- 4') through stack ducts C.

. The top of the pit chamber 0 is U ually covered by a cover 0 which is removed to permit I the insertion. and removal 'of ingots C1 by a crane hoist.. The cover, in the case of a batch heating operation as .is contemplated herein, is

removed when the batch of hot ingots is removed, and replacedatter a batch of cold ingots is inserted inthe pit. The cold ingots may be copper. steel or other metal depending uponthe circumstances; and should be heated to a The control system of Fig. 1 includes two control instruments B and A, each of a form described more in detail in connection with Fig. 2, and responding respectively to the temperature on the top surfaceof an ingot within the pit, and to the temperatur of the bottom and inside of an ingot within the pit. With suitably distributed heating of the pit it is immaterial which ingot is selected for either thermocouple T or T which thermocouples are the temperature sensitive elements respectively responsive to ingot top temperature and ingot inside bottom temperature, and connected to instruments A and B. If the heatv distribution is uneven, special ingots may be selected for the thermocouples. If for example the ingots S (see Fig. 4) which are in the path of the hot gases between the burner port and outlet ducts, are under some conditions hotter than the other ingots, the thermocouple T should be associated with one of those, and preferably with the hottest of those ingots. Under those conditions the thermocouple T' should ingots. It should be understood that the use of the terms hottest or coolest ingots is made templates respectively the ingot most quickly affected on a change in fuel supply and the ingot most slowly affected on a change in fuel supply.

The instruments A and B together control the position of a fuel valve by means of the fluid operated motor Q, the latter under direct control of the instrument A, which regulates the control pressure in pipe PQ accordingly as the temperature of the ingotbutts or bottoms varies from a predetermined value. Fluid under pressure is supplied to instrument A from a pipe A0 If the supply of fluid pressure to the instrumentA were constant, the control. of valve Q would be solely in accordance with the butt temperature, but the supply pressure to instrument A is not constant under all conditions, but at times is L regulated by the .instrument B. Instrument B is supplied with a substantially constant fluid pressure through a pipe 0 and four way valve 0 The valve 0 normally connects the pipe PQ with instrument A, and places supply pipe O in communication with a suitable source of pressure 0 regulated by pressure regulator Instrument B through means later described, regulates the pressure in pipe A0 supplying instrument A, in accordance with the variations in temperature at the ingot top, whereby the final regulating effect upon valve motor Q is in joint accordance with the ingot top and ingot butt temperatures.

It is desirable to maintain the ratio between the volume of fuel supplied and the volume of air supplied. To this end either the "semi-metered controller of Fig. 1 or the fully metered controller of Fig. 4 may be used. In Fig. 1, a device W is employed which is responsive to the differfor convenience of description, and actually conential pressure across an orifice D in the fuel lin D and responsive therefore, to the rate of flow of fuel, to move a flapper valve W with respect to a nozzle W and thereby control the supply of fluid pressure to a damper motor W supplying combustion supporting air to chamber C Nozzle W is supplied with pressure from a suitable source W through restriction W to control the pressure in pipe W connected to the damper motor W. In Fig. 4 a flow metering device U is employed to measure th duel flow and a flow metering device V is employed to measure the air flow, these meters being adapted to actuate a ratio flow controller WA and adjust fluid pressure motor W, controlling the supply of air as necessary to maintain the desired volumetric ratio between fuel and air. Since the present invention is not concerned with ratio fiow control means such apparatus need not be described in detail here, but is generally described to make plain that it is immaterial in respect to this invention whether as shown, the fuel valve is controlled by the novel control apparatus, and the supply of air is proportioned thereto, or whether the air valve is controlled by this apparatus and the fuel proportioned to the air. Limitations in the field, arrangement of fuel and air lines and the like will normally determinewhich arrangement is used, so that in referring to control of fuel either air or gas or other fuel in contemplated.

The instruments A and B may take different forms, and as shown in Fig. 1, each comprises a potentiometer recorder pneumatic controller. The potentiometer instrument shown comprises a recorder carriage F movable horizontally in one direction and the other by the rotation of a helically grooved or screw threaded shaft F in threaded engagement with the carriage F. A potentiometer instrument of the type shown, comprises a relay mechanism controlled by the defiection of a galvanometer pointer G for automatically adjusting a potentiometer measuring circuit resistance H when and as required to rebalance the measuring circuit, and forrotating the shaft F to adjust the carriage F longitudinally of the shaft into positions corresponding to the different values of the quantity measured, and the variations of which produce defiections of the galvanometer pointer G. For example the galvanometer of the instrument A is connected in circuit with the thermocouple responsive to the ingot butt temperature, and is arranged so that the voltage of the thermocouple is opposed to a variable portion of a source of standard voltage H depending on the adjustment of the contact I-I along the resistor H.

The mechanism by which the potentiometer measuring circuit is rebalanced and the shaft F is rotated to adjust the carriage F, need not be further described herein as its particular form constitutes no part of the present invention, which is adapted for use withmeasuring and control instruments of very different forms. It is noted however that the particular potentiometer instrument mechanism shown, may be of the form employed in the Brown potentiometer" instrument which is in extensive commercial use,

and the characteristics of which, in the precise form herein illustrated, are disclosed in my pending application Serial No. 75.704 filed April 22, 1936, now Patent No. 2,159,971, issued May 30, 1939.

The control provision of the instrument shown include a so-called control table I cooperating The control 'tablelnormally occupies a fixed D I with the recorder carriageF. The table I is a sheet metal'stru'cture supported by a shaft 1'.

sition along the path of movement of the recordercarriage F, but may be adjusted along that path. To affect its adjustment, the-shaft I" may bearotatable helically grooved or threaded shaft in threaded engagement with the table -A control member F is pivotallyconnected to the part 1 is a roller;

As the recorder carriage F moves to the left, as seen in Fig. 2, nomovement is givento the f ontrol table part B so long as; the horizontal edge portion 1 is in engagementwiththe roller left hand end of the edge portion 1 the control table part I turns down under the action of gravity or other suitable bias force,.to the extent permitted by the engagement of the-innormal control range of the instrument, in which its control effect varies with "the position of. the carriage 'F, is that required for movement of the roller F into and onto! engagement with the edge portion 1 When its movement to the left carries the roller F? out of engagement with 0n a movement of the pen carriage to the right of the position in which it engages edge I I part I will be retained in its adjusted position by means described in my-above-mentioned copending application Serial No. 75,704, 'andneed not be described here.

-The up and down movement of the control table part F gives corresponding movement to a control bar 6 having its underside bearing against the control table part P and prevented from separating from the latter, by a guide part I". The control bar J extends between the two, end plates E and is connected at its ends to arms J each pivotally connected to the adjacent edge plate E by a pivot J coaxial with the pivot for the control table part I. The left arm J, shown in Fig. 2, is provided with a transverseportion J adapted to engage the upper edge of the adjacent end plate E, and thus arrest the down passage. The lower end of the link M carries an actuating abutment formed by anut M, which is adlustably secured in place on the link by a lock nut M.

The vertical movements of the abutment M give movements to the actuating elements N of the control apparatus located. in the compart ment (1'. As shown, the actuating element N is a lever having a horizontally disposed arm formed with a slot N at its free end through which the link M passes. The lever N has a gravitational bias for movement in the counter-clockwise direction, as seen in Fig; 2, so that its slot ted end is'supported by the abutment nut M and follows the up and down movements of the latter. I

The control apparatus through which the iongitudinal movements of the link M produce control eii'ects 'by'giving movements to the actuat- F, but as the roller F moves awayfrom the clined edge portion 1, with the roller The the edge portion 1, iurther down movement of the control table-part1 is prevented by means hereinafter described.

iing element Nfimay take various forms. shown the control'apparatus is an air actuated pivot NR'.'. duce control effects by m'ovinga flapper valve controller, ot a idifm which is fully disclosed in the Coleman Big- Moore Patent No. 2,125,081, granted July 26,. 193%}, and is now inextensive commercial use The lever N is pivoted at N to an adjustable fulcrum member NR, in the form of a lever F having, a stationary fulcrum The movements of the lever N pro-o O away "from or permitting it to approach a nozzle or bleed orifice member 0 valve 0 is mounted on a stationary pivot 0 and is biased for movement in the direction in which it approaches and restricts the discharge through the nozzle 0 The lever acts on the flapper 0 through a pin N carried by a depend:

movement of thecontrol bar J and control table part I, as the recorder carried roller F moves to the left, as seen in Fig. 2, of the edge portion I.

The measuring and controlinstrument actuates the associated control -Tapparatus; as hereinafter described, through a link L having its upl per end pivotally connected to an extension J" connected to transverse member J andhaving I example, instrument A, and in register with said ing arm of the lever.

The nozzle 01 receives air froma. pipe 0 through a restricted passage formed by a small bore; pipe P included in a pilot valve mecha} nlsm P, so that the pressure in the nozzle 0 which constitute the primary control pressure of the control apparatus, increases and decreases as the flapper, valve 0 moves toward and away from the nozzle.

wall-P of that chamber is movable, and separates the chamber P from a second pilot valve chamber 1?. The pressure in the latter is regulated by a valve P actuated by the said movable wall P The pressure in the chamber P is thus maintained in constant proportion to the pri-' mary control pressure in the chamber P and constitutes the ultimate'control pressure of the apparatus. The ultimate control pressure'of instrument A is'transmitted by pipe PQ to the de-'-. vice to be controlled, which as shown in Fig. 2,

A, however, as previously indicated, but controls. the supply of fluid to theinstrument A, the pipe A0 of the instrument B corresponding to the pipe PQ of instrument A being con- [nected to pipe 0 ofthe instrument A. As will be understood, pipe 0 of the instrument'B is connected to a suitable source Q of constant fluid pressure. a

The ultimatecontrol pressure in both instruments A and B is also transmitted by pipe PR.

' to mechanismR, iorming a part or, the control apparatus, and adapted, following and as aresuit oi. each initial changein theultimate con The primary .control pressure is transmitted by a pipe 0 to'a chamber P of the pilot valve mechanism. One

trol pressure, effected through link M, to give the lever NR an initial follow up adjustment, and a delayed compensating adjustment. The follow-up adjustment neutralizes a portion of the initial adjustmentof the flapper valve effected by the link M. The delayed compensating adjustment slowly neutralizes more or less of the effect-of the preceding follow up adjustment.

The mechanism R comprises bellows elements two of which are connected :by a connected rod R, which carries a projection R The latter acts on lever NR through a lever R pivoted at R, and a pin it interposed between the levers R. and NR. The pin R is supported by a lever Ft pivoted at R toa member R adjustable to vary theleverage with which the lever R. acts on the lever NR. The latter is biased for movement in the clockwise direction, as seen in Fig.

2. Adjustment of the member R, which may be effected by rotation of member R is a so-called throttling adjustment by means of which the ratio of a movement of carriage F to the resulting ultimate pressure change is determined.

Details of the construction and operation vof the mechanism R, not specifically referred to herein, will be understood by those skilled in the art from the drawings, and need not be described F of instrument A to the right, the bar J will be raised. This will give an up movement to the link M, and will adjust the lever N clockwise, as seen in Fig. 2, whereupon the flapper valve 0 will move away from the nozzle 0 and decrease the primary and ultimate control pressures. The resultant decrease in the pressure in the pressure chamber of the motor Q will give a closing adjustment to that motor, reducing the rate of fuel supply to the furnace and thereby tending to restore the temperature to its normal value. Such an increase in temperature of the ingot top temperature and movement of the recorder carri'rge F of instrument B to the right will result in a decrease in pressure of the supply fluid to instrument A through pipe A0 and pipe 0 of instrument A. On a decrease in supply pressure to instrument A tire pressure in chamber P will fall and the net effect, of the reduction in pressure in the chamber P as well as the supply pressure, will be a reduction in the ultimate control pressure in pipe PQ and valve motor Q wherebya reduction in the rate of fuel supply is effected. The relative control pressure change on motor Q- resulting from a given movement of the carriage F of instrument A or of instrument B may be separately predetermined by. adjustment of the member R individual to each of those instruments. Such capacity for individual proportioning of the amount of control pressure change on a variation respectively in the ingot top temperature and the ingot bottom temperature is practically important because it is ordinarily desirable to rapidly cut down the fuel supply on a rise in ingot top temperature while a slower decrease in the fuel supply is often permissible on a rise in ingot bottom temperature.

, Conversely, on a decrease in either ingot butt or ingot top temperature, the corresponding carriage F will move to the left, as seen in Fig. 2, and thereby give a down movement to the individual link vM and a closing adjustment to the individual flapper valve 0. The resultant increase in the control pressures will produce an opening adjustment of the valve Q and an increase in the rate of fuel supply to the furnace,

tending to restore the temperature to its normal value.

Valve 0 may be alternatively adjusted to connect the pipe 0 directly with the pipe PQ and disconnect both instruments A and B from the latter.. With such adjustment the position of motor Q is controlled by manual adjustment of screw 0 of the regulator O by means of which the pressure in pipe PQ is manually adjusted as may be necessary under abnormal conditions. In normal operation regulator 0 determines the maximum operating pressure and thereby the limit of movement of motor Q in the opening direction.

A by-pass valve 0 is also provided by means of which instrument B may be eliminated from operation when, as is normally the case, valve 0 connects pipe 0 with pipe 0 and pipe PQ with instrument A. Under normal conditions the instrument A may be by-passed or rendered inoperative by opening by-pass valve 0 With valve 0 fully open and valve 0 closed the motor Q will be under sole control of instrument A, while with valve 0 fully open and valve 0 closed the motor Q will be under sole control of instrument B.

The apparatus 01 Fig. l, in which only one thermocouple T is shown, may be modified by installing a thermocouple T in conjunction with a plurality of or all the ingots, in which case such thermocouples may be connected to respond to the average of the temperatures of the ingot butts as shown in Fig. 1C. The thermocouples may be connected in parallel for this purpose as the thermocouples of Fig. 4 are connected. Thermocouple T of Fig. 1 may also be supplemented by thermocouples associated with a plurality or all of the ingots and so connected as to give a measure of the average ingot top condition as shown in Fig. 10. Alternatively, a plurality of thermocouples T- maybe associated with respective ingots and connected to independent controllers like the instrument B as shown in Fig. 1A, or may be successively connected to a single instrument as shown in Fig. 1B.

In Fig. 1A, the supply pressure to instrument A is controlled by two instruments B, the latter being connected together as the instruments A and B of Fig. 1 are connected together. In con- I sequence the final control pressure to which motor Q is subjected will depend on the effects produced respectively by all the instruments B and by the instrument A, the throttling adjustment R of each instrument establishing the respective effect which each instrument will have on.

the total effect.

In Fig. 1B a motor operated selector switch X is employed, forming a portion of the instrument B and arranged to successively connect thermocouples T in circuit with the instrument scribed in exactly th same rotating motor x5 energized sum it suitable source. oi current X, X. I: desired a. switch x may be opened manually by means ofwhich supply conductor X is. interrupted .unless a switch X in branch conductor X is then closed.

meta- Switch X may be opened by'means hereinafter described in, connection with Fig. 5 when any thermocouple '1 reaches a predetermined temperature, preventing the selector switch, from making instrument B responsive to another thermocouple I so long as switch X -is open. Instrument. B in the apparatus of Fig. 113 will thus be successively responsive to :thermocouples T1 and will remainresponsive to the first thermocouple to reach a predetermined temperature until said thermocouple again falls below the preaccount the highesttemperature of each of the ingots and the lowest temperature of each of the ingots, or in the form using the highest temperature of a representative 'ingot or the lowest temperature of a representative ingot; common ,soaklng pit construction does not facilitate the proper placing of the thermocouples and it is more practicable to employ the apparatus of Fig. 3v in which radiation pyrometers are employed in lieu of the thermocouples of Fig. 1."

In Fig. 3, radiationpyrometers Y and Y of knowniorm and comprising athermal junction focused uponthe ingots at the desired points, are used and correspond effectively to the ther mocouples T and T respectively. As will be clear,

the radiation pyrometers may be connected in the circuits of Figs. 1, 1A, 1B and of ig. 4, later demanner as the thermocouples T and '1".

In Fight and 4A, is illustrated a un further embodiment ofthe invention in which the thermocouple T of Fig. 1 isarranged, not incontact with an ingot butremoved vertically therefrom, and projecting through the cover. So placed,

the] temperatures of the tops of all the ingots.

.Thel'ajrrangement of thermocouple? of Fig. 4: has the practical advantage of anticipating a rise fiarneor combustion gas-temperature, which will be felt by thermocouplefr'ef; before the ingot top temperature, change takes place. r

Also'in Fig. 4, the thermocouples T are placed in: the ducts C instead of within the ingots as .in the ii'eld. In Fig. 5 the pen carriages FD and FC, incorporated respectively in instruments AA and BB corresponding to instruments .A and 13, maybe adjusted substantially in the manner in which pen carriage F of Fig. 2 is adjusted, re-

sponsive respectively to the temperatures of thermocouples T' and 'I or radiation devices Y and Y The defiections of the pen carriages FD and FC, however, do not produce fluid pressure eil'ects through the mechanism including bell crank lever N of Fig. 2, 'but'produce electrical efi'ects' generally equivalent to and replacing those fluid pressure eifects. The lever N of each instrument AA and BB, the pivot Wot-which is fixed, is adapted to carry a plurality of contact arms a, a a 'anda or b, b, b and b (see Fig'ZA) cooperating with the electrical apparat s of Fig. 5, and replacing the fluid pressure apparatus comprising parts 0, P, Q, and R of Fig. 2; which are omitted from Fig. 5. In Fig. 5 the dotted-lines connecting carriages FD and FC with their respective contacts represent the linkage such as J, L, M and N of Fig. 2, which may be employed to connect the carriages and contacts in the apparatus diagrammatically shown in Fig. 2A.

This linkage should preferably include throttling range adjusting provisions by means of whichthe extent of the electrical effect produced by a given movement of carriageFC; or FD is individually predetermined, because normally the effect resulting from a movement of carriage FC will desirably be difierent from that resulting from an equal movement of carriage" FD. To this end and as will beclear from Fig.

2B, the point of attachment of link L to lever thermocouple '1 is. significantly responsive to .in'ingot top temperatures following a rise in inFig. 1, and although when so placed, they are 1 affected by radiation from the-recuperators and by the outgoing gases, I findthatyin many cases at least; the response is sufllciently significant to the coolest ingot temperature to provide a reliable, index corresponding to the thermocou- -ple T of Fig. 1. The correspondingly identified parts of Fig. 4 correspond to the like parts of l v Fig. 1, although as previously described the fuelair control means of Fig. 4 is different from those 0! Fig.1. r l r I Fig. 5 illustrates a preferred embodiment of the invention, in which functions attained with r the fluid pressure operated apparatus of Fig. .1 are attained with electrical control apparatus, and in addition certain practically important adjustments are provided in a form which con- L' is made adjustable toward and away from the axis of shaft L, the extent of up or down movement of link M in response to a movement of link L depending upon that adjustment. As

shown, the link L is attached to a part L adjustable in slot L of lever L and clamped in the desired. position by screw L Another slot L is provided in the lever L' on the opposite side of the axis of shaft L from. slot L to a1 'ternately accommodate part- L?, whereby the direction of the control'efiect produced by niovemerit of link L may be reversed.

The apparatus of Fig. 5 ultimately controls. the

fuel or air valve QA corresponding to the valve Q of Figs. 1, 2' and 3, such control being effected in part by the cooperation-of contacts a, a of the instrument AA and contacts b, b of the instrument BB with the same electrical network, whereby continuous responsiveness to each of the significant conditions is attained. Contacts a,

a respectively engage and are adjustable along resistors 0 and a" and contacts b, b respectively engage and are adjustable along resistors b and 12 Resistors a and b are disposed on one side of a mid resistor ab and resistors a" and-l are disposed on the opposite side of the resistor ab, all the resistors being connected in a series circuit across a pair 'of line conductors I and 2, supplying a suitable source of energizing current. Another resistor3 is connected in parallel with the series resistor circuit and an equalizing conductor 5. extends between a contact 6 engaging and adjustable along resistor 3, and a contact I engaging and adjustable along resistor ab. The resistors and conductors just referred to form in effect a bridge circuit adapted to .be

unbalanced by adjustment of resistors a", a",

bi", b or '3, causing a difference in potential tribute to"simpliflcation and easeof adjustment between contacts 6 and i which causes an un equal flow of current respectively in a pair of opposed solenoid coils 8 and 9 which are connected each at one end to a line wire I or 2and connected together at theiropposite ends and to conductor 5. The coils& and 9 are inductively related to ari armature to, which is moved toward coil 8 or toward coil 9 depending upon the direction of unbalance, and is adapted to control a contact member I I. Contact member I I is connected to line conductor 2, and is arranged to engage one or the other of a pair of contacts I 2, I3 when armature I is deflected. Contacts I2 and I3 are connected respectively to fields It, It of a reversible electrical motor, and the opposite ends of the field windings are connected together and to line conductor I. Motor 56 is connected through suitable gearing to actuate valve QA and is also connected to move contact 5 along resistor 3. The direction of rotation of motor I6 on an unbalance of the bridge, is such as to adjust contact 5 in a direction to restore the balance.

If the apparatus did not extend beyond that already described, it would include control of valve QA jointly from instruments AA and BB. On a movement of contacts a and a to the left in response to a decrease below its predetermined normal value of the bottom ingot temperature, fuel valve QA will be opened to increase that temperature. If the top of ingot temperature simultaneouslydrops below its normal temperature, the resulting fuel correction will be in the same direction but if the ingot top temperature increases simultaneously and suitably with the decrease in ingot butt temperature, the effects will cancel out and no fuel correction will be made. 'The total resistance in the arms including resistors a b a and b, will remain constant notwithstanding adjustment of the resistors individually, which feature is made possible by the arrangement of the-contacts with respect to their resistors and the symmetrical arrangement of the resistors on either side of contact I. On an adjustment of contacts a and a or contacts b and b the resistance removed from the arm to one side of the contact I will be equal to the resistance added to the arm on the opposite side of the contact, whereby equal movements of the contacts in different portions of their range of movement will produce substantially equal valve movements. A resistor I8 is shown in the circuit to the left of contact i,

which is employed to limit the travel of the valve QA, and is adjustable by means of contact I9 4 adjusted by a'manually adjustable knob 20 connected in a suitable manner to the contact I9. The resistance I8 does not significantly upset the symmetry of the circuit just referred to, but any such effect could be eliminated by placing a similar resistance and adjustable contact on the opposite side of contact I and arranged for operation simultaneously with contact I9.

In a stable control system such as the one just described and without the load compensating feaature'control employing load compensating or reset means not inconsistent with the other requirements 'of the control system, as is the case with other load compensating means now known. For example, it is desirable, in the control application for which this system is intended, to effect a load compensating adjustment in a direction to reduce the fuel supply if either the ingot butt temperature or the ingot top temperature is too high, but it is desirable to effect a load compensating adjustment in 'a direction to increase the fuel supply only if both of those temperatures are low.

For purposes of compensating the system for load variations 1 have shown in Fig. 5, electrical load compensating or reset provisions including a motor 2i coupled to adjust contact "I which in the apparatus described to this point, has been considered stationary. Motor 2I is provided with two fields 2|L and 28H respectively adapted to rotate the motor in a direction to move contact i to the left and to the right thereby increasing or decreasing the fuel supplyt The motor 2| is energized through circuits including contacts a, a and b b of instruments AA and BB, the contacts being deflected in accordance with the variations in ingot top and ingot butt temperatures, and cooperating with stationary contacts a, a and 17 b. When contacts a a and 12 b are undefiected, as they will be when both temperatures are normal, no circuits will be closed. When contact b is deflected to the right on a rise in ingot butt temperature, a circuit will be closed to field ZIH from line 2 to switch 22, through the latter when closed to conductor 23, contacts b and b conductor 24, field ZIH to line I. right on a rise in ingot top temperature, a circuit will be closed for field 28H from line 2, conductor 25, switch 26', conductor 21, contacts a and a and conductor 28, field 2IH to the line conductor I. Thus contact I is moved to the right respons'ively to' a rise in either the ingot butt temperature or the ingot top temperature, to thereby effect a closing adjustment of valve QA.

On a deflection of contacts a and b to the left, a circuit is closed from the line wire 2, contacts a and a, conductor 29, switch 30, conductor 3|, contacts b and b field 2IL to line I, but this circuit can be effected only upon defiection of both contacts a and b to the left, contacts a and b both being deflected to the left only when both the ingot top and the ingot butt temperatures are low.

The switches 22, 26 and 30 respectively controlling the circuits above traced, are unnecessary with the proper proportioning of the motor 2i and with the proper gear relation between the latter and the contact "I, but for purposes of adjustmentadapting the apparatus to specific practical requirements, those switches are employed and are closed during a relatively fixed but manually adjustable time period. Switches 22 and 30 are mounted on bracket 32 pivoted at 33, and the bracket 32 is provided with a roller 34 in engagement with cam 35. Cam 35 is driven by a unidirectional motor 36 energized from the line wires I and 2, and provided with speed adjustment 31, Switch 26 ismounted on a bracket 38 pivoted at 39, a roller 40 of the bracket being adaptedto be engaged by cam II driven by a second unidirectional motor 42 also energized from line wires I and 2. The speed of motor 42 is controlled by an adjustable resistor and con- When contact a is deflected to the .Taaemaeo tact at, and the speed adjustment devices :1. and

63 are controlled respectively by manual adlusting dials M and t5, the angular adjustment of said dials determining the time period ofclosure of switches-22 and 30 and respectively, forming in effect means by which the load'compensatlon or reset efiect produced by adjustment of the contact 1, and injected into the collective control action, is proportioned to the duration of departure of the ingot top and ingot butt temperatures from. their respective normal values. I: it is desired to make, the-extent of movement of the contact 1 dependent not only upon the direction of deflection 'of moving contacts a and a, b and b but-upon the extent of defiec tion, the stationary contacts a, a", 11 and b may be formed of material of a relatively high electrical resistance, whereby the speed of rotation of'themotor 2| will depend not only upon the existing adjustment of devices 31 and 43, but uponthe extent of deflection of the movable contacts.

For purposes of manual adjustment of the extent of ultimate control effect resulting from a given movement of the various resistors, a resistor ab is provided which is shunted about resistor ab and is provided with manually adjustable knob ab connected by suitable means ab to movable contact ab whereby more or less of the resistor ab, is shunted about resistor ab Tl'le rate and/or extent of movement of motor 2!" is also preferably individually adjusted by means of speed control adjusting resistor 2|A more or less of which is connected in series with motor 2| depending upon the existing adjustment of contact MB. The latter is adjusted by means of knob ZID through suitable means ZIC. Though I have disclosed in the foregoing,

simultaneously operating means for adjusting the All fuel valve in-joint response to ingot top temperature and ingot butt temperature, such joint response need not be simultaneous but may be successively effected through a single instrument such as instrument A when provided with selector means such as switch X. With such an arrangement the switch X may alternately connect the top thermocouple and the butt thermocouple in circuit with the instrument whereby successive matic control apparatus controlled by electrical measuring means, which are disclosed but not claimed herein, are claimed in my prior applicaa combustion heating means for passing hot gases of combustion through the chamber and over the articles wherein those portions of the articles which are contacted first by the hpt gases of combustion are heated and brought up to temperature A at a faster rate than those portions of the articles measuring and control is attained such as is diswhich are contacted last by the hot gases of combustion, comprising in combination, a plurality of temperature responsive devices positioned respectively to respond significantly to the temperature of a corresponding one of the articles at that portion thereof which is contacted last by the hot gases of combustion, temperature averaging means actuated by said devices to respond to an average of the temperature to which said devices respond, temperature responsive means positioned to respond significantly to the temperature of those portions of the articles which are contacted first by the. hot gases of combustion, control means for the combustionheating means, and

means controlled by the temperature averaging means and the temperature responsive means for controlling the control means for heating the articles uniformly and rapidly as possible to a desired temperature without injury to the articles.

, 2. A control apparatus for a metallurgical iurnace having a heating chamber-in which a plurality of articles to be heated are placed and having a combustion heating means for passing hot gases of combustion through the chamber and over the articles wherein those portions of the articles which are .contacted first by. the hot gases of combus-tion are heated and brought up to temperature. at a faster rate than those portions of the articles which are contacted last by the hot gases of combustion, comprising in combination, a plurality of temperature responsive devices positioned respectively to respond significantly to the temperature of a. corresponding one of the articles at that portion thereof which is contacted last by the hot gases of combustion, temperature averaging means actuated'by said devices to respond to an average of the temperature to which said devices respond, at second plurality of temperature responsive devices positioned respectively to respond 5 significantly to the temperature of a correspond actuated by said second temperature responsive devices to respond to an average of the temperature to which said devices respond, control means tion Serial No. 101,063, filed Sept. 16, 1936, now

Patent No. 2,201,946, issued May 21, 1940.

While in accordance with the provisions of the I statutes, I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent tothose skilled in'the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention as set forth in the apv pended claims and that in some cases certain features of my invention may be used to advanfor the combustion heating means, and means controlled by the ,firstand second temperature averaging means forcontrolling the control means for heating the articles uniformly and rapidly as possible to a desired temperature without injury to the articles.

3. A control apparatus for a metallurgical furnace having a heating chamber provided with a central bottom inlet ground which a plurality of articles to be heated are placed and having a combustion heating means for passing hot gases of combustion through the bottom inlet vertically to tage without a corresponding use of other features. r, v Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. A control apparatus for a metallurgical fur-. nace having a heating chamber in which a pluralimpinge the roof of the heating chamber and thereby diverted downwardly along the articles and exhausted through aplurality of bottom outlets wherein the top portions of the articles adjacent the roof are heated and brought up to temperature at a faster rate than the bottom portions of the articles adjacent the bottom outlets, comprisingin combination, a plurality of temper-y ature responsive devices positioned adjacent the outlets of the heating chamber respectively to ity of articles to be heated are placed and having .75 respond significantly to the temperature of a cortemperature responsive means positioned adjacent the roof of the heating chamber to respond significantly to the temperature of the top portions of the articles, control means for the combustion heating means, and means controlled by the temperature averaging means and the temper ature responsive means for controlling the control means i or heating the articles uniformly and rapidly as possible to a desired temperature without injury to the articles.

4. A control apparatus for a metallurgical furnace having a heating chamber provided with a central bottom inlet around which a plurality of articles to be heated are placed and having a combustion heating means for passing hot gases of combustion through the bottom inlet vertically to impinge the roof of the heating chamber and thereby diverted downwardly along the articles and exhausted through a plurality of bottom outlets wherein the top portions of the articles adjacent the roof are heated and brought up to temperature at a faster rate than the bottom portions of the articles adjacent-the bottom outlets, comprising in combination, a plurality of temperature responsive devices positioned adjacent the outlets of the heating chamber respectively to respond significantly to the temperature of a corresponding one of the articles at the bottom portion thereof, temperature averaging means actuated by said devices to respond to the average of the temperature to which said devices respond, a second plurality of temperature responsive devices positioned adjacent the roof of the heating chamber respectively to respond significantly to the temperature of a corresponding one of the articles at the top portion thereof, second temperature averaging means actuated by said second devices to respond to the average of the temperature to which said devices respond, control means for the combustion heating means, and means controlled by the first and second temperature averaging means for controlling the control means for heating the articles uniformly and rapidly as possible to a desired temperature without injury to the articles.

ANKER E. KROGH. 

